The present invention relates to a process for the production of a range of improved biomass material products, and in particular to the improvement of a biomass material which has been formed as a bi-product from the treatment of municipal solid waste (MSW). The invention further relates to an apparatus for the production of such range of improved biomass material products and the range of biomass materials produced thereby. The biomass material products produced are particularly suitable for use as a fuel for power generation, gasification, hospitals, industrial heating and domestic heating. The biomass materials products produced are suitable as an alternative fuel to fossil fuels, or standard biomass fuels formed from for example shredded dried wood and/or grass.
Incineration is a previously known method for the disposal of MSW. MSW generally comprises a combination of waste materials such as paper, vegetation, food, rubbers, textiles, wood, leather, plastics, glass and metals, or could contain waste from commercial outlets for example fast-food restaurants having a substantial mix of food, plastics and paper. Combustion of the MSW produces a heat energy which, for example, can be used to produce electricity. However, burning produces ash and noxious fumes which must be contained and further processed to enable their safe disposal.
Many governments now place restrictions on the burning of fuels in order to strictly limit the amount of noxious substances released into the environment. It is therefore desirable to process the MSW in a manner which enables the separation and recovery of inorganic and organic material therefrom. The separated organic material after further processing can then be used as a fuel which can be burnt in an environmentally more friendly manner.
Traditionally it is known to separate the organic and inorganic matters by saturating the MSW with water and/or steam, whilst heating and rotating the MSW to cause pulping of the organic material therein. The treated organic matter is then separated from the inorganic components of the waste by allowing it to fall through a screen. Examples of such processes are described in U.S. Pat. Nos. 5,190,226 and 5,556,445. However, these known processes provide a pulped organic matter with a water content of between 35% to 70%, which is extremely wet and therefore further processing is required to reduce the water content to render the pulp suitable for use as a compost or fuel. Also, the pulped material will still contain some non-combustible material such as metals, rubble, glass etc, and combustible toxic materials such as plastics and rubbers which are of a size which has enabled their passage through the perforations of the screen with the thus recovered organic matter. The presence of such non-combustible material and toxic materials reduces the value of the biomass fuel produced from the recovered organic material, since burning of such fuel still results in the production of some noxious gas and ash, lowering its potential energy density.
International Patent Application No. WO 03/092922 describes an improved method for the treatment of MSW which provides an organic pulped material having a moisture content of up to 15% which is highly suitable for further processing to produce a fuel or compost. However, the improved organic pulped material is still separated from the non-organic components of the waste by its passage through a trommel screen, and thus still contains some non-organic and toxic components.
Air separators are known which use two flows of air to separate out material based on its density. One such system is known from EP 0982082 (Beloit Technologies Inc). In this prior system air is drawn through a vertical separation chamber which is open to the atmosphere. Material to be separated is introduced into the rising stream of air and material having a lower density rises with the uprising air, whilst heavier material falls through the open bottom of the separator. The dispersion of the material is accomplished with a jet of high pressure air which breaks up and disperses the material within the rising air stream. This system is particularly adapted to separate wood chips, with the more dense knotted chips falling through the uprising current of air and, with the lighter chips being drawn up the separation chamber. However, this system is unsuitable for separating MSW. This is because MSW contains items such as glass shards, which although possessing a relatively high density also have a relatively large cross-sectional area which would enable them to be captured by the high pressure jet and forced up the separation chamber, rather than falling down to the outlet for collection.